Paper sheets, such as bills and securities, include sheets on which fluorescent images applied with fluorescent ink or the like for authentication are formed. Irradiation of such a paper sheet with ultraviolet light causes the fluorescent image to emit light. Accordingly, the paper sheet can be authenticated through reading the light-emitting fluorescent image.
Patent Literature 1 discloses an optical line sensor device that includes an ultraviolet light LED light source to read a fluorescent image. In the optical line sensor device in Patent Literature 1, a filter that cuts off visible light having wavelengths of 410 nm or less and ultraviolet light is disposed between an object to be illuminated and an image sensor, thereby improving the capability of detecting the fluorescent image.